Andrews P C, Pubols M H, Hermodson M A, Sheares B T, Dixon J E
J Biol Chem. 1984 Nov 10;259(21):13267-72.
The 22-residue somatostatin (SST-22) from channel catfish, purified by an improved method, is shown to be a glycopeptide. This represents the first report of a glycosylated somatostatin. Multiple forms of SST-22 exist with the major form containing 1 mol of galactose and 1 mol of N-acetylgalactosamine/mol of peptide attached via an O-glycosidic linkage to Thr-5. The position of the carbohydrate was determined by trapping the reactive peptide following beta-elimination of the carbohydrate with [35S]beta-mercaptoethanol followed by sequencing of the radiolabeled protein. All forms of SST-22 that have been purified are identical in amino acid composition. The heterogeneity resides in the carbohydrate portion of the glycopeptide with at least one of the minor forms containing sialic acid. The sequence for SST-22 obtained by automated Edman degradation is Asp X Asn X Thr X Val X Thr X Ser X Lys X Pro X Leu X Asn X Cys X Met X Asn X Tyr X Phe X Trp X Lys X Ser X Arg X Thr X Ala X Cys. This sequence differs at positions 5 and 19 from that published by Oyama et al. (Oyama, H., Bradshaw, R. A., Bates, O.J., and Permutt, A. (1980) J. Biol. Chem. 255, 2251-2254). The amino acid sequence reported here is identical to that deduced from the cDNA. The mass ion of SST-22 was determined by fast atom bombardment/mass spectrometry and shown to be 2943 +/- 1 (m/z). The observed mass ion is consistent with the molecular weight predicted from the amino acid sequence plus 1 mol of galactose and 1 mol of N-acetylgalactosamine.
通过改进方法纯化得到的来自斑点叉尾鮰的22个氨基酸残基的生长抑素（SST - 22）被证明是一种糖肽。这是关于糖基化生长抑素的首次报道。SST - 22存在多种形式，主要形式为每摩尔肽含有1摩尔半乳糖和1摩尔N - 乙酰半乳糖胺，通过O - 糖苷键连接到苏氨酸 - 5上。通过用[35S]β - 巯基乙醇对碳水化合物进行β - 消除后捕获反应性肽，然后对放射性标记的蛋白质进行测序，确定了碳水化合物的位置。所有纯化得到的SST - 22形式在氨基酸组成上是相同的。异质性存在于糖肽的碳水化合物部分，至少有一种次要形式含有唾液酸。通过自动埃德曼降解获得的SST - 22序列为天冬氨酸X天冬酰胺X苏氨酸X缬氨酸X苏氨酸X丝氨酸X赖氨酸X脯氨酸X亮氨酸X天冬酰胺X半胱氨酸X甲硫氨酸X天冬酰胺X酪氨酸X苯丙氨酸X色氨酸X赖氨酸X丝氨酸X精氨酸X苏氨酸X丙氨酸X半胱氨酸。该序列在第5和19位与Oyama等人发表的序列不同（Oyama, H., Bradshaw, R. A., Bates, O.J., and Permutt, A. (1980) J. Biol. Chem. 255, 2251 - 2254）。这里报道的氨基酸序列与从cDNA推导的序列相同。通过快原子轰击/质谱法测定了SST - 22的质量离子，结果显示为2943 +/- 1（m/z）。观察到的质量离子与根据氨基酸序列加上1摩尔半乳糖和1摩尔N - 乙酰半乳糖胺预测的分子量一致。
